Hydrostatic and Vibration Test System for a Blowout Preventative

ABSTRACT

A method and apparatus for testing blowout preventers for leaks involves maintaining a constant pressure in the portion of the blowout preventer to be tested. A sensor is connected to a controller for maintaining a constant pressure within the blowout preventer. Any amount of fluid introduced into or removed from the blowout preventer in order to maintain constant pressure is measured and is an indication of the leak rate in the blowout preventer.

REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 62/140,795 filed Mar. 31, 2015, the enter contents of which isincorporated herein by reference thereto.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is directed to a method and apparatus for testinghydraulically actuated safely systems such as blowout preventers forleaks.

2. Description of Related Arts Invention

Oil and Gas Exploration risk management includes the ability to controlsubsurface pressures which may be encounter during drilling operation.The primary mechanism utilized by operators to control downholepressures is the hydrostatic pressure as a result of the drilling fluidcontained within the wellbore. The drilling fluid is engineered andformulated to a density that provides a hydrostatic pressure inside ofthe wellbore that is greater than the formation pressure being drilled.In the majority of drilling operations, the hydrostatic control ofwellbore pressure is adequate. However, from time-to-time the operatormay encounter a higher than expected formation pressure where there isnot adequate hydrostatic pressure to control the wellbore pressure.During these times the operator relies on a series of mechanicalcontrols to stabilize the wellbore and prevent a “Blow Out”. A blow outis the uncontrolled release of fluid or gas from the wellbore. Thisevent is extremely dangerous and therefore must be avoided if at allpossible. The primary mechanical control device utilized by operators tocontrol wellbore pressure is the Blowout Preventer (BOP) assembly. TheBOP assembly consists of multiple sealing and shearing devices that arehydraulically actuated to provide various means of sealing around thedrill string or shearing it off entirely, completely sealing thewellbore. It is essential that the BOP assembly operate as designedduring these critical operations. Therefore it is a regulatoryrequirement to test the functionality and the integrity of the BOPassembly before starting drilling operations and at specific eventsduring the drilling operations. The BOP assembly test is a series ofpressure tests at a minimum of two pressure levels. low pressure andhigh pressure. During the pressure test, intensifying fluid from a highpressure intensifying pump unit is introduced into the BOP assembly in avolume sufficient to cause the internal pressure within the BOP assemblyto rise to the first pressure test level. Once the first pressure testlevel is established the high pressure intensifying pump unit isisolated from the BOP assembly and the pressure is monitored for atleast five minutes. Current regulations require that the pressure doesnot decay at a rate greater than 5 psi/minute or 25 psi total over theentirety of the five minute test. Upon successful completion of thefirst test a subsequent high pressure test is performed. The requirementfor the high pressure test is the same as the lower pressure test. Thepressure decay rate must not exceed 5 psi/minute or 25 psi total overthe entirety of the five minute test. These tests are generally referredto within the industry as a hydrostatic test. Hydrostatic testing is avery well know and established practice and testing of BOP assemblieshas been a required test for many years. The equipment utilized toperform the test has not changed over the years and is very dated. Thetypical fixed displacement hydrostatic test system utilizes a highpressure triplex plunger intensifying pump, driven by a diesel motor.The fixed displacement hydrostatic test system features a clutchassembly and a reduction gearbox between the diesel motor and the highpressure triplex intensifying pump. The drive ratio between the dieselmotor and high pressure triplex intensifying pump is fixed and cannot beadjusted or changed once the hydrostatic test has been initiated. Somefixed displacement hydrostatic test system utilize an electric motor andvariable frequency drive in place of the diesel motor and clutch, butotherwise operate similarly and have the same limitations related totheir fixed displacement design. Additionally, the fixed displacementhydrostatic test system utilizes at least one pressure gauge and onechart recorder. The pressure gauge depicts the test pressure and thechart recorder records the pressure over time. The technician controlsthe pressure and pump rate by varying the diesel engine speed and byengaging or disengaging the clutch. Some units feature a multiple ratioreduction gearbox to increase the controllability of the fixeddisplacement hydrostatic test system when performing low flow rate test.The gearbox ration is manually selected by the technician and must beset before the test is performed. The entire hydrostatic test ismanually controlled by the technician. A successful test relies entirelyupon the skill of the technician and his ability to control the fixeddisplacement hydrostatic test system and interpret the pressure gauge.The reliance on the skill of technician and the lack of automation andcomputerization to enhance controllability makes the testing processproblematic. In addition the mechanical chart recorder lacks thenecessary resolution to make definitive pass or fail decisions. Thisrequires the technician to utilize their skill and judgment whendeciding if the BOP passed or failed the hydrostatic pressure test.

A more specific description of the currently utilized fixed displacementhydrostatic test system will reveal further short comings. Adisadvantage of the currently utilized fixed displacement hydrostatictest system is the size of the high pressure triplex intensifying pumpand the horsepower require to operate it. During a typical BOP assemblyhydrostatic test the rate at which the intensifying fluid is pumped intothe BOP assembly varies greatly with pressure. Initially the BOPassembly may contain substantial amounts of uncompressed air. Thereforethe initial pump rate of a typical closed BOP assembly hydrostatic testmight be 10 GPM but will decrease exponentially as the air iscompressed. The “GPM” series of the chart in FIG. 1 depicts theexponential decrease of pump rate in relation to the pressure increaseduring a typical 10,000 psi BOP assembly hydrostatic test. Additionally,the “Horsepower” series of the same chart depicts the theoreticalhorsepower requirement related to the pump rate at the same pressurewith the equation:

Horsepower=Pump Rate (gpm)×Discharge Pressure (psi)/1714.

As clearly depicted in FIG. 1 the pump rate exponentially decreases aspressure increases and at approximately 1,000 PSI the pump rate is lessthan 1 GPM. Typical high pressure triplex intensifying pumps currentlyutilized in fixed displacement hydrostatic test systems applicable toBOP assembly testing have a maximum operating speed of 600 rpm. Thedisplacement of the high pressure triplex intensifying pump is relatedto the maximum operating speed and the maximum designed pump rate. Atypical 10 gpm high pressure triplex intensifying pump designed tooperate at 600 rpm will have an approximate displacement of 3.85 cubicinches per revolution “cir”. The displacement of the high pressuretriplex intensifying pump is fixed and therefore the torque to rotatethe high pressure triplex intensifying pump at 10,000 psi is:

Displacement (cir)×Pressure (psi)/75.4=3.85×10,000/75.4=510.61 ft-lbstorque.

Therefore, the theoretical horsepower to drive the high pressure triplexintensifying pump can be calculated with the equation:

RPM×Torque (ft-lbs)/5252=600×510/5252=58.26 HP.

This differs greatly from the actual horsepower required and is a resultof the fixed displacement design. Typical fixed displacement hydrostatictest systems do not provided a means of matching the displacement andthe required pump rate. Therefore the torque requirement of the fixeddisplacement hydrostatic test system increase linear with pressure. Therelationship between torque and pressure for the fixed displacement pumpis depicted in FIG. 2. Another disadvantage of the fixed displacementhydrostatic test system is the lack of displacement resolution at higherpressures. For example, to pressure a BOP assembly, with an initial airvolume of 10 gallons, from 1,000 psi to 10,000 psi only requiresapproximately 0.15 gallons of additional intensifying fluid to be addedto the BOP assembly. This is less than 1 revolution of the high pressuretriplex pump currently utilized on typical fixed displacementhydrostatic test systems. This is very difficult to control and thefinal pressure is often overshot. If the overshoot is large enough thetest must be repeated. A typical state-of-the-art fixed displacementhydrostatic test system is approximately 10 ft long×5 ft wide and 5 fttall. It is powered by a 75 hp diesel motor and weighs approximately5,000 lbs. Also note the fixed displacement hydrostatic test system ismanually operated with no provision for computerized operation or datacollection. A typical hydrostatic test cycle utilizing a typical fixeddisplacement hydrostatic system commences with the technician pumpingintensifying fluid at a high flow rate until the pressure gaugeinitially responds to the increasing pressure within the BOP system.

Once the initial volume of air is compressed (very low pressure) thepressure will increase very rapidly. Therefore, due to the lack ofdisplacement resolution, the technician will begin to “bump” the fixeddisplacement hydrostatic test system to achieve the final pressure.“Bumping” is practice or technique where the technician cycles the fixeddisplacement hydrostatic test system on and off as quickly as possibleusing the clutch. This practice or technique relies heavily on the skillof the technician and can be very problematic and time consuming. It isalso very easy to overshoot the test pressure. If the test pressure isexceed by a specified amount the test will not be valid and must beperformed again. Lastly, the results are recorded on a manual chartrecorder. The chart recorder is a very crude way of recording the testpressures and pressure decay rate (psi/min). A typical chart recorderhas a resolution of 250 or 500 psi per line segment. While the chartrecorder does provide a record of the BOP assembly hydrostatic test. itdoes not provided data about the actual leak rate.

As previously mentioned the current regulations, related to theintegrity of the BOP assembly, requires the BOP to have a decay rate ofless than 5 psi/min or 25 psi total over the entirety of the five minutetest. It is reasoned by the regulators that if a BOP has a decay rateless than or equal to the maximum allowed by the regulation then it doesnot have a volumetric leak rate sufficient enough to compromise thefunctionality and integrity of the BOP assembly. Another reason forusing a pressure decay model for BOP testing was the lack of anyeconomically viable technology with a resolution capable measuring thevolumetric loss related to leak rate. The loss of fluid associated witha leak of sufficient size to cause a 5 psi/min decay rate is miniscule.It could be less than 0.00002 GPM depending on the amount of air in theBOP assembly during the initial phase of the test. Measuring theseextremely low flow rates accurately utilizing conventional flow metersis not practical or in some cases even possible. It is also evident thatmeasuring the leak rate by monitoring the rate of pressure decay isinherently inaccurate. For example: if a typical BOP assembly with avolumetric loss rate (leak) of approximately 0.000008 gpm is firsttested with approximately 5 gallons of air trapped within the BOPassembly during the initial phase of the hydrostatic test andsubsequently tested with the same volumetric loss rate (leak) but withapproximately 2.5 gallons of air trapped within the BOP assembly duringthe initial phase of the hydrostatic test, the BOP would pass the firsttest with approximately a 3 psi/min pressure decay rate but it wouldfail the second test with approximately a 6 psi/min pressure decay rate.Each test would have the same volumetric loss rate (leak) but the resultof the tests would be significantly different. The effects of reducedinitial air volumes in the BOP assembly increase substantially until atsome point the pressure decay rate test will not be a viable means ofleak detection. If the BOP assembly is hydraulically locked it will notbe possible to utilize a pressure decay hydrostatic test. It is sometimethe practice of the hydrostatic test technician to add air to the BOPassembly to ensure testability. This practice, while ensuringtestability of the BOP assembly, will most likely lead to erroneousresults as previously discussed above. Additionally, the resolution ofthe recorder makes it difficult to ascertain the actual pressure decayrate and the decision of pass/fail is mostly that of the technician'sinterpretation of the data. Subsequent to obtaining a successful testthe chart recorder paper is signed and submitted as proof that the BOPassembly meets or exceeds the pressure decay rate specifications of theapplicable regulations. Lastly. the entire intensified circuit isrelieved of the intensified fluid via the dump valve. The typical dumpvalve is a manually operated needle or tapered plug valve.

Metal seat valves are used due to the extreme fluid velocities acrossthe valve seat when the intensified fluid is released. Additionally, theintensified fluid flowing back from the BOP assembly carriescontaminates such as sand and grit picked up from the BOP assembly.These valves must be serviced often to ensure the metal seat have notbeen comprised by the intensified fluid release. The much preferredcurrent available soft seat designs lack the integrity to providereliable service in this harsh service.

Consequently, there is a need for an improved hydrostatic test systemthat provides for fully variable displacement and is compact and easilyportable. Such a system should also include a computer or processor tocontrol and automate the test cycle and provide for useful data such asleak rate and other environmental and mechanical properties of the BOPAssembly. Additionally the test data should be electronically stored andeasily disseminated via local and wide area networks in real-time orsubsequent to the completion of the test.

BRIEF SUMMARY OF SOME OF THE PREFERRED EMBODIMENTS

The present invention addresses these and other needs by providing afully variable displacement hydrostatic test system that features avariable displacement hydraulic pump driven by an electric, air,internal combustion motor, or other suitable motivation. The variabledisplacement hydraulic pump provides a fully variable source of energyand therefore a fully variable drive ratio between the motivator and theintensifying pump(s). The intensifying pumps may be of linear or rotarydesign and may be equipped with a means of precisely measuring thevolume discharged. The variable displacement hydrostatic test systemautomatically varies the intensifying pumps displacement based onpressure and flow feedback from the system to optimize the displacement.This allows for a repeatable, highly accurate, and responsivehydrostatic test. Another desirable benefit of displacement optimizationassociated with the variable displacement hydrostatic test system is thereduced physical size and reduced energy requirement. The variabledisplacement hydrostatic test system requires less than 5 horsepower toachieve the flow and pressure requirements of a typical hydrostatic testas compared to the 75 horsepower of the fixed displacement hydrostatictest system. FIG. 3 depicts the theoretical horsepower required by thevariable displacement hydrostatic test system where the intensificationrate is approximately 50 psi/second. Another advantage of the variabledisplacement hydrostatic test system is the ability to match therequired torque or force required by the intensifying pumps to that ofthe motivator. FIG. 4 depicts the torque or force required at theintensifying pumps and that required by the motivator for the samepressure. As depicted in FIG. 4 the force or torque required by theintensifying pumps is linear to pressure while the force or torque atthe motivator remains constant. This feature allows the variabledisplacement hydrostatic test system to use the power from the motivatormuch more efficiently than fixed displacement hydrostatic test systems.Additionally the variable displacement hydrostatic test system has amuch greater displacement resolution than the currently utilized fixeddisplacement hydrostatic test system. For example, if the displacementof the variable displacement hydrostatic test system is manipulated tohave a displacement 0.3 cir then the system will have approximately 10times the displacement resolution as the fixed displacement hydrostatictest system. The fully variable feature of the variable displacementhydrostatic test system allows for displacements from 0.0 cir to maximumdesigned cir. The variable displacement hydrostatic test system is muchmore controllable than the fixed displacement hydrostatic test systemand significantly reduces the chance of overshooting the final testpressure. In addition the efficiencies described previously allow for amuch more compact design. A variable displacement hydrostatic testsystem equivalent in performance to the previously described fixeddisplacement hydrostatic test system would have dimensions of 48″wide×60″ long×34″ tall and weighs approximately 800 lbs.

Based on the algorithms subsequently described and using thedisplacement optimized intensifying pumps in conjunction with thecomputer processor to monitor and control the system in real time allowsfor a very precise, quick, and repeatable test that does not rely on theskill of the technician for completion or interpretation. The entiretesting process is performed, based on the testing parameters, withoutintervention of the technician. Another feature of the variabledisplacement hydrostatic test system is the ability of the computerprocessor to store, and/or relay to a remote location, the test resultsfor analysis or oversight. This allows for independent 3rd partyverification of the BOP hydrostatic test. Additionally, the data can belogged with specific data about the BOP assembly such as serial number,rig number, and test location to help predict future BOP performance ormaintenance requirements. The variable displacement hydrostatic testsystem features a novel and unique method of measuring the volumetricloss rate by offsetting the volumetric loss rate within the BOP assemblywith sufficient intensifying fluid to maintain the test pressure aspreviously described above. An embodiment of the variable displacementhydrostatic test system features linear intensifying pumps that areequipped with a precision electronic transducer that precisely measuresthe displacement and subsequent volume of test fluid introduced into theBOP assembly allowing for direct measurement of the volumetric loss rateand pressure decay rate associated with all potential sources. Severaladvantages of utilizing the variable displacement hydrostatic testsystem in conjunction with the novel algorithms, subsequently describedbelow, become apparent when applied to complex BOP assemblies. Currenttechnology is limited to very simplistic pressure decay ratemeasurements only. The largest potential source of pressure decay, otherthan leakage, is the change in temperature of the trapped air, theintensification fluid, and the BOP assembly. Utilizing current fixeddisplacement hydrostatic testing technology it is necessary to wait fora period of time until the temperature stabilizes to obtain a validtest. This is a direct result of the lack of automation and displacementresolution of currently utilized fixed displacement systems. This cantake several minutes or even hours. Today, the daily cost of a typicalland base drilling rig can exceed $75,000 and offshore rigs can exceedUS $350,000. A delay of a few hours can be very costly. The variabledisplacement hydrostatic test system utilizes a computer processorrunning a novel and unique algorithm applied to the resultantdisplacement measurements from the linear intensifying pumps, equippedwith precision electronic transducers, at various test pressures, tomathematically isolate the leak rate component from the other potentialsources of volumetric and pressure decay changes. This is possiblebecause the leak rate is a nonlinear function of pressure, while thepressure decay rate due to temperature change is approximately linearwhen the test pressure is held constant over a short period of time. Thenonlinear behavior of the leak rate is defined by Bernoulli's Principlewhere the velocity is proportional to the square root of differentialpressure. Additionally the ability of the improved hydrostatic system toprecisely measure the total volumetric loss over a period of time at afixed pressure eliminates or mitigates other sources of volumetric andpressure decay changes. This is significantly different than currenttechnology where the pressure is allowed to decay over time. Thisintroduces linear and nonlinear changes to the pressure decay rate dueto flexibility of the BOP assembly and adiabatic related changes to theair volume within the BOP assembly as the pressure decays. The abilityof the improved hydrostatic test system to automatically maintain aconstant pressure by either adding test fluid or removing test fluidfrom the BOP assembly in conjunction with the ability of the improvedhydrostatic test system to precisely measure the amount of fluid addedor removed is a unique and desirable capability. This capability allowsfor complete isolation of the linear and nonlinear responses applicableto the entire BOP assembly at a specific pressure. This unique featureallows for utilization of other technologies to identify the present ofleak and possible the location of a leak. One such technology is theutilization of vibration instrumentation such as accelerometers oracoustic sensors to detect the location and amplitude of minutevibrations emitted by the test fluid passing from the high pressureregime to the low pressure regime across the leak path. This is knowntechnology and is widely utilized by municipalities and large industrialprocessing plants. In these applications the process stream (pressuresource) is stable and can be monitored over long periods of time toestablish benchmarks. These benchmarks can then be used to detect andvariants. However migrating this technology into the field of BOPpressure testing has been problematic and to date unsuccessful. Incontrast to fixed location municipalities and large industrialprocessing plants, BOP assemblies are mobile and their processingprofile is ever changing. The improved hydrostatic test system providesfor a method of first testing at a constant pressure and then at adifferent constant pressure. The vibration profile of the BOP assemblycan then be compared at the two pressure level to identify the specificchanges to the profile related to leak paths within the BOP assembly.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter that form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand the specific embodiments disclosed may be readily utilized as abasis for modifying or designing other embodiments for carrying out thesame purposes of the present invention. It should also be realized bythose skilled in the art that such equivalent embodiments do not departfrom the spirit and scope of the invention as set forth in the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of the preferred embodiments of theinvention, reference will now be made to the accompanying drawings inwhich:

FIG. 1 is a graph showing the relationship between horsepower and flowrate verses pressure

FIG. 2 is a graph showing the relationship between the torquerequirement of a fixed displacement pump and pressure in the prior art.

FIG. 3 is a graph showing the relationship between horsepower andpressure in a test system utilizing variable displacement pump.

FIG. 4 is a graph showing the relationship between the torques of forcerequired by the motor for the same pressure.

FIG. 5 is a schematic of a variable displacement hydrostatic test systemaccording to an embodiment of the invention.

FIG. 6 is a schematic of a second variable displacement hydrostatic testsystem according to a second embodiment of the invention.

FIG. 7 is a schematic showing of a control system for the test apparatusof FIG. 5 or 6.

FIG. 8 is an algorithm processed in a computer processor.

FIG. 9 is a second algorithm processed in a computer processor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of a variable displacement hydrostatic test system 10 isshown in FIG. 5. It includes a variable displacement hydraulic pump 12driven by a suitable power source 18 such as an electric motor. Pump 12is connected to a reservoir 42 containing hydraulic fluid. The pressureof fluid from the hydraulic pump is controlled by a valve 14 in a mannerknown in the art. Fluid from pump 12 enters intensifying pump 20 viavalve 50. Intensifying pump 20 is connected to a source of water, orother suitable intensification fluid 45, via conduit 48.

Water under pressure exits intensifying pump 20 via a check valve 76 andenters a primary linear intensifying pump 26 which is driven byhydraulic fluid from hydraulic pump 12 via valve 51 and from there to asecondary linear intensifying pump 28 also driven by hydraulic pump 12via valve 52. Hydraulic fluid from variable displacement pump 12provides a variable energy source via valves 50, 51 and 52 at a rate andpressure required for operation of pumps 20, 26, and 28 in accordancewith the requirements of pressure and flowrate shown in FIG. 1. A checkvalve 78 is positioned between pumps 26 and 28.

Hydraulic energy from variable displacement hydraulic pump 12 can bedirected to dump valve 44 via valve 53 for operation as required. Rotaryintensifying pump 20 is in fluid communication with water intake port 22via conduit 48. Rotary intensifying pump 20 is in fluid communicationwith primary high pressure check valve 76, primary linear intensifierpump 26, and secondary linear intensifier pump 28, secondary highpressure check valve 78, dump valve 44, pressure transducer 40, conduit46, and BOP assembly 24. Rotary intensifying pump 20 is of a positivedisplacement piston design. Intensifying fluid is displaced into BOPassembly 24 via conduit 46 to intensify the internal pressure of BOPassembly 24. Primary linear intensifying pump 26 intensifies theinternal pressure within the BOP assembly 24 from a pressure test pointto a subsequent higher pressure test point. Secondary intensifying pump28 maintains the test pressure during the volume loss/pressure decayanalysis phase of the hydrostatic test. Pressure transducer 40 providesa high resolution electronic signal representative of the pressurewithin BOP assembly 24. Dump Valve 44 relieves the intensified fluidwithin BOP assembly 24. Primary linear intensifying pump 26 andsecondary linear intensifying pump 28 are equipped with precisionelectronic transducers 30 and 32 respectively which precisely measuresthe displacement of linear intensifying pumps 26 and 28. Vibrationsensor or sensors 76 measure the energy level of vibration signalsassociated with vibration signals of the BOP assembly. The electronicsignals from displacement transducers 30 and 32, pressure transducer 40and vibration sensor 76 are communicated to computer processor 34 asshown in FIG. 7. The computer processor 34 is an integrated component ofa control system 36, which includes HMI (Human Machine Interface) 38.The control system 36, including an HMI are further integrated intovariable displacement hydrostatic test system 10.

Describing a typical test cycle of a variable displacement hydrostatictest system, hydraulic fluid from the variable displacement hydraulicpump is first provided at a rate and pressure sufficient for operationof the rotary intensifying pump in accordance with the requirements ofthe pressure/flow curve. The rotary intensifying pump is used tointensify the internal pressure of the BOP assembly to a first lowpressure to substantially reduce the volume of air within the BOPassembly. Additionally the variable displacement hydrostatic test systemmay include at least one linear intensifying pump. The primary linearintensifying pump 26 intensifies the internal pressure within the BOPassembly from a pressure test point to a subsequent higher pressure testpoint. The much smaller secondary intensifying pump 28 is used tomaintain the test pressure during the volume/pressure decay analysisphase of the hydrostatic test. It is important to note, that undercertain environmental conditions, it may be necessary to reduce thevolume of intensification fluid within the BOP assembly to maintain anapproximate constant pressure within the BOP assembly. Theseenvironmental conditions most commonly occur where the BOP assembly isexposed to direct sunlight causing the BOP assembly to become warmerthan the ambient environmental temperature. Subsequently, whenintensification fluid, which is very near the ambient environmentaltemperature, is added to the BOP assembly to cause a pressure increase,heat is transferred from the BOP assembly to the intensification fluidcausing the intensification fluid to increase in volume and thereforerequiring intensifying pump 28 to reduce the volume of intensificationfluid to maintain an approximately constant pressure within the BOPassembly. Secondary intensifying pump 28 is specifically designed toallow for, and precisely measure, the addition or reduction ofintensification fluid as may be required to maintain an approximatelyconstant pressure within the BOP assembly. The linear intensifiers allowfor very finite and precision displacement resolution. The linearintensifying pumps are equipped with a precision electronic transducers30, 32 that precisely measure the displacement of the linearintensifying pump. This method of measuring is extremely precise withvery fine resolution allowing for accurate determination of the volumeof intensifying fluid displace into the BOP assembly. The precise amountof intensifying fluid displacement is continuously monitored andcontrolled by an on-board computer processor.

A method of using variable displacement hydrostatic test system 10 mayinclude the steps of: (1) deploy variable displacement hydrostatic testsystem 10; (2) confirm proper operation and startup of variabledisplacement hydrostatic test system 10; (3) perform hydrostatic test;(4) confirm and disseminate results of the hydrostatic test; (5) safelyshut down variable displacement hydrostatic test system 10; and (6)decommission and prepare for transport variable displacement hydrostatictest system 10.

Deployment of variable displacement hydrostatic test system 10 in step(1) may include positioning variable displacement hydrostatic testsystem 10 in a convenient location which provides safe access to BOPassembly 24 and the required utilities. Connecting the requiredutilities and high pressure conduit 46 between variable displacementhydrostatic test system 10 and BOP assembly 24 to provide for a fluidconnection between variable displacement hydrostatic test system 10 andBOP assembly 24. Confirming proper operation and startup of variabledisplacement hydrostatic test system 10 in step (2) may includeenergizing variable displacement hydrostatic test system 10. Verifyingproper operation of control system 36. Hydrostatic testing utilizingvariable displacement hydrostatic test system 10 step (3) may includesetting the desired final test pressure according to the hydrostatictest specifications, and energizing electric motor 18 which furtherenergizes variable displacement hydraulic pump 12. Variable displacementhydraulic pump 12 features integrated control valve 14. Integratedcontrol valve 14 is of a modulated design where an electronic signalgenerated by computer processor 34 varies the output pressure ofvariable displacement hydraulic pump 12 in direct proportion to thesignal generated by computer processor 34. Energizing variabledisplacement hydraulic pump 12 provides a variable hydraulic energysource. Close dump valve 44 by directing energized hydraulic fluid todump valve 44. Dump valve 44 is in fluid communication with conduit 46at a position between secondary intensifying pump 28 and BOP assembly24. Initiate automated hydrostatic test cycle utilizing computerprocessor 34. Testing and collection of data via computer processor 34is continuous but comprises distinctly different phases. Phase 1initializes the automated hydrostatic test. Phase 2 and phase 3 arerepeated two or more times throughout the intermediate portion of thehydrostatic test and phase 4 is performed subsequent to obtaining thefinal test pressure. Phase 1 of the automated hydrostatic test cycle mayinclude diverting energized hydraulic fluid to rotary intensifying pump20 at a rate and pressure in accordance with a specified pressure/flowcurve of the hydrostatic test. An example of a typical pressure/flowcurve is depicted in FIG. 1. Intensification fluid provided at intakeport 22 is pumped and intensified by rotary intensifying pump 20 to BOPassembly 24 via conduit 46. BOP assembly 24 responds to the incomingintensified fluid both environmentally and mechanically asintensification increases. The pressure changes associated with theresponse to the intensified fluid are measured with pressure transducer40. Pressure transducer 40 is in fluid communication conduit 46 at aposition between secondary high intensifying pump 28 and BOP assembly24. The responses are analyzed in real time by computer processor 34utilizing common equations applicable to pressure drop and ideal gaslaws computed through specific algorithms to calculate thecompressibility factor of BOP assembly 24. The results of phase 1 testare recorded by computer processor 34 and depicted on HMI 38. At aspecific test pressure identified by computer processor 34 utilizing thecompressibility factor calculated during phase 1 the energized hydraulicfluid is isolated from rotary intensifying pump 20. Secondary highpressure check valve 78 prevents intensifying fluid from escapingconduit and therefore intensified fluid remains intensified. Commencingphase 2, energized hydraulic fluid is directed to primary linearintensifier 26 via valve 51 at a rate and pressure in accordance with aspecified pressure/flow curve. At a specific test pressure identified bycomputer processor 34 utilizing the compressibility factor calculatedduring phase 1 the energized hydraulic fluid is isolated from primarylinear intensifier 26. The displacement of primary linear intensifier 26is measured utilizing precision electronic transducer 30. Themeasurement is recorded and time normalized to calculate rate of changeby computer processor 34. The rate of change is utilized by computerprocessor 34 to refine the compressibility factor of BOP assembly 24previously calculated during phase 1. Secondary high pressure checkvalve 78 prevents intensifying fluid from escaping conduit 46 andtherefore intensified fluid remains intensified. Commencing phase 3,Energized hydraulic fluid is directed to the secondary linearintensifier 28 via valve 52 at a rate sufficient to maintain intensifiedfluid in conduit 46 at a specific test pressure approximately 50 psiabove the highest pressure obtained during the immediately previousphase 2 test for a period of approximately 30 seconds. At the conclusionof the test period, energized hydraulic fluid is isolated from secondarylinear intensifier 28. The displacement of secondary linear intensifier28 is precisely measured utilizing precision electronic transducer 32.The measurement is recorded and time normalized to calculate rate ofchange by computer processor 34. Subsequently computer processor 34utilizing one or both of the algorithms depicted in FIGS. 8 and 9,calculates the leak rate, if any, at the test pressure by solving theequations:

√(P2/P1)=(V2−Lf)/(V1−Lf)

Where: P1=Base Pressure (psi)=first test point in the previouslydescribed test sequence.

P2=Test Pressure (psi)=subsequent test points following the initial basetest point.

V1=Base Volume (gpm)=volume added at base test pressure to maintain basepressure adjusted for time period.

V2=Test Volume (gpm)=volume added at subsequent test points to maintaintest point pressure adjusted for time period.

Lf=the volumetric flow rate of the linear time decay component of thetotal volumetric decay rate.

Solving the above equation for any test point in comparison with thebase test point will find the volumetric decay rate associated withtemperature and other linear volumetric decay rates. Subsequently thenonlinear leak rate can be found with the equation:

Nf=V2−Lf

V2=Test Volume (gpm)=volume added at subsequent test points to maintaintest point pressure adjusted for time period.

Lf=the volumetric flow rate of the linear time decay component of thetotal volumetric decay rate.

Nf=the volumetric flow rate of the nonlinear time decay component of thetotal volumetric decay rate.

The first cycle of phase 2 and phase 3 are considered the base cycle.The subsequent cycles of phase 2 and phase 3 are considered the testcycles. The results of phase 2 and phase 3 tests are recorded bycomputer processor 34 and depicted on HMI 38. Phase 2 and phase 3 arerepeated by a number of times determined by computer processor 34, butnot less than once. Preferably at least one secondary test would beperformed at a pressure level equal to twice the pressure of the basetest. Secondary high pressure check valve 78 prevents intensifying fluidfrom escaping conduit 46 and therefore intensified fluid remainsintensified. Phase 4 is conducted at the final test pressure. Duringphase 4 the pressure reading from pressure transducer 40 are recordedover a specific time period determined by computer processor 34, but notless than 1 minute. The results of phase 4 test are recorded by computerprocessor 34 and depicted on HMI 38. Phase 4 is optional and dependenton the requirements of the hydrostatic test specifications. Phase 4 isconsider to be equivalent to the currently utilized pressure decay testtypical of currently utilized fixed displacement hydrostatic testsystems. Subsequent to the completion of the hydrostatic test. dumpvalve 44 is de-energized. De-energizing dump valve 44 de-intensifiesintensified fluid in conduit 46. Return intensification fluid receivedfrom BOP assembly 24 is directed away from variable displacementhydrostatic test system 10 via the dump valve 44 to a suitable reservoir49. Dump valve 44 is of a soft seat design making it liquid tight whichis essential for successful testing. Any leak at dump valve 44 would beinterpreted by computer processor 34 as a potential leak of BOP assembly24.

An additional embodiment 60 of the invention is shown in FIG. 6. Commonelements from the embodiment of FIG. 5 have the same reference numerals.

In this embodiment the intensifying pump 26 which is of a well-knowndesign includes a plunger 62 located in a hydrostatic chamber 63. Apiston 69 is attached to the plunger 62 and is positioned within thehydraulic chamber 61.

A variable displacement hydraulic pump 12 which is driven by a primemotive source such as an electric motor 18 drives intensifier pump 26via hydraulic lines 66 and 65 which are connected to the hydraulic powerchamber 61 on either side of piston 69.

Variable displacement pump 12 may be of the type having a variable swashplate the position of which is controlled by a valve 14 in a mannerknown in the art.

Water from a reservoir 45 is drawn into hydrostatical chamber 63 throughcheck valve 84 on the intake stroke of plunger 62 and is then directedto the blowout preventer 24 via check valve 85 and a conduit 46 duringthe exhaust stroke of the pump.

Pressure sensor 40 is located in conduit 46 and dump valve 44 isconnected to conduit 46 for relieving pressure within the blowoutpreventer. One or more vibration sensors 76 are attached to the blowoutpreventer at various points to detect vibrations caused by leakagethrough the various components of the blowout preventer.

This embodiment utilizes a single pump for pressurizing the blowoutpreventer, however a plurality of pumps may also be used. The same pumpcan also be used to maintain the pressure within the blowout preventerduring the test to measure the addition of any fluid necessary tomaintain constant pressure within the portion of the blowout preventer.

Should the pressure decrease during the test, controller 34 as a resultof a signal from pressure transducer 40 will send a signal to valve 14to increase the pressure from variable displacement pump 12 as depictedin FIG. 7. This will cause piston 69 of intensifier pump 63 to move afinite distance which corresponds to the amount of fluid added to theblowout preventer in order to maintain constant pressure. This distanceis sensed by sensor 64 and the information is sent to controller 34 forprocessing.

Additionally vibration analysis may be performed in conjunction with orseparately from the just previously describe automated hydrostatic testusing the same unique constant pressure test methodology. Morespecially, an automated hydrostatic test that includes vibrationanalysis may include setting the desired final test pressure accordingto the hydrostatic test specifications. Energizing electric motor 18energizes variable displacement hydraulic pump 12. Variable displacementhydraulic pump 12 features integrated control valve 14. Integratedcontrol valve 14 is of a modulated design where an electronic signalgenerated by computer processor 34 varies the output pressure ofvariable displacement hydraulic pump 12 in direct proportion to thesignal generated by computer processor 34. Energizing variabledisplacement hydraulic pump 12 provides a variable hydraulic energysource to hydraulic chamber 61. Close dump valve 44 by directingenergized hydraulic fluid to dump valve 44. Dump valve 44 is in fluidcommunication with conduit 46 at a position between secondaryintensifying pump 28 and BOP assembly 24. Initiate automated hydrostatictest cycle utilizing computer processor 34. Testing and collection ofdata via computer processor 34 is continuous but comprises distinctlydifferent phases. Phase 1 initializes the automated hydrostatic test.Phase 2 and phase 3 are repeated two or more times throughout theintermediate portion of the hydrostatic test and phase 4 is performedsubsequent to obtaining the final test pressure. Phase 1 of theautomated hydrostatic test cycle may include diverting energizedhydraulic fluid 74 to rotary intensifying pump 20 at a rate and pressurein accordance with a specified pressure/flow curve of the hydrostatictest. An example of a typical pressure/flow curve is depicted in FIG. 1.Intensification fluid provided at intake port 22 is pumped andintensified by rotary intensifying pump 20 to BOP assembly 24 viaconduit 46. BOP assembly 24 responds to the incoming intensified fluidboth environmentally and mechanically as intensification increases. Thepressure changes associated with the response to the intensified fluidare measured with pressure transducer 40. Pressure transducer 40 is influid communication with conduit 46 at a position between secondaryintensifying pump 28 and BOP assembly 24. The responses are analyzed inreal time by computer processor 34 utilizing common equations applicableto pressure drop and ideal gas laws computed through specific algorithmsto calculate the compressibility factor of BOP assembly 24. The resultsof phase 1 test are recorded by computer processor 34 and depicted onHMI 38. At a specific test pressure identified by computer processor 34utilizing the compressibility factor calculated during phase 1 theenergized hydraulic fluid is isolated from rotary intensifying pump 20.Secondary high pressure check valve 78 prevents intensifying fluid fromescaping conduit 46 and therefore intensified fluid remains intensified.Commencing phase 2, energized hydraulic fluid is directed to primarylinear intensifier 26 via valve 51 at a rate and pressure in accordancewith a specified pressure/flow curve. At a specific test pressureidentified by computer processor 34 utilizing the compressibility factorcalculated during phase 1 the energized hydraulic fluid is isolated fromprimary linear intensifier 26. The displacement of primary linearintensifier 26 is measured utilizing precision electronic transducer 30.The measurement is recorded and time normalized to calculate rate ofchange by computer processor 34. The rate of change is utilized bycomputer processor 34 to refine the compressibility factor of BOPassembly 24 previously calculated during phase 1. Secondary highpressure check valve 78 prevents intensifying fluid from escapingconduit 46 and therefore intensified fluid remains intensified.Commencing phase 3, Energized hydraulic fluid is directed to thesecondary linear intensifier 28 via valve 52 at a rate sufficient tomaintain intensified fluid at a specific test pressure approximately 50psi above the highest pressure obtained during the immediately previousphase 2 test for a period of approximately 30 seconds. During the 30second period, measurements from at least one vibration sensor 76 butpreferably more than one vibration sensor 76 are recorded by computerprocessor 34. At the conclusion of the test period, energized hydraulicfluid is isolated from secondary linear intensifier 28. Phase 2 andphase 3 are repeated two or more times throughout the intermediateportion of the hydrostatic test. At the conclusion of the testingutilizing phase 2 and phase 3, computer processor 34, using commonlyavailable vibration analysis algorithms, identifies differences betweenthe base test and subsequent test. Specifically computer processor 34identifies differences in the energy level of the vibration signalsbetween the base test and subsequent test. It is known within theindustry that the energy level of the vibration signals of waterturbulent flow passing from a high pressure regime to a low pressureregime is approximately proportional to the differential pressurebetween the high and low pressure regimes. Therefore it would be anindication of a leak if the energy level of the vibration signalincrease approximately proportional to the increased pressure.Conversely it would be an indication of the absent of a leak if theenergy level of the vibration signal remained principally the samethought the series of different pressure level test.

Confirmation and dissemination of the results of the hydrostatic teststep (4) may include transfer of applicable hydrostatic data, viainformation technology system 19, onto portable media or transfer vialocal and/or wide area networks both wired and wireless. Confirmationmay include acceptance the test by a 3rd party at the location or aremote location. Shut down of variable displacement hydrostatic testsystem 10 step (5) may include operation of the emergency stop.Decommissioning variable displacement hydrostatic test system fortransportation step (6) may include disconnection and storage ofutilities and disconnection and storage of high pressure hose 46.

While a preferred embodiment of the present invention has been describedit is meant as illustrative only and not limiting in scope. A full rangeof equivalents, many variations and modification, may be naturallyoccurring from those skilled in the art after review hereof.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations may be made herein without departing from the spirit andscope of the invention as defined by the appended claims.

For example an electric cylinder embodiment of the system utilizeselectrically operated cylinders that offer the same extend and retractfunctionality of the hydraulic cylinders. They are usually of a ballscrew design to reduce friction and accommodate high working forces.Additionally the electric motor utilized is capable of full torque atzero speed. The primary electric cylinder is mechanically coupled to awater intensification cylinder. The dump valve electric cylinder ismechanically coupled to the dump valve. There is a pressure sensor influid communication with the water intensification cylinder.Additionally the water intensification cylinder is in fluidcommunication with a water source, the dump valve, and the BOP Assembly.In operation, an electric source is precisely controlled by a motorcontroller, such as a variable frequency drive, commanded by a computercontroller, to cause both the primary electric cylinder and the dumpvalve electric cylinder to extend. The action of the dump valve electriccylinder extending causes the dump valve to close. The action of theprimary electric cylinder extending causes the water intensificationcylinder to displace water intensification fluid into the BOP Assemblythereby causing a pressure increase within the BOP Assembly. This actionof displacing water intensification fluid.

Causing pressure increase within the BOP assembly, continues until thepressure within the BOP Assembly reaches the desired pressure level.Subsequent to reaching the desired pressure level, the computercontroller precisely controls the torque of the electric motor drivingthe primary electric cylinder to maintain the pressure within the BOPAssembly at a constant pressure at or very near the desired pressure.Subsequent to completing the test the primary electric cylinder iscommanded to the fully retracted position. The dump valve electriccylinder is commanded to the fully retracted position, causing the dumpvalve to open, releasing the test pressure from the BOP assembly.

An air cylinder embodiment of the system utilizes air operated cylindersthat offer the same extend and retract functionality of the hydrauliccylinder except that the hydraulic power source is replaced with apressurized air source. The primary air cylinder is mechanically coupledto a water intensification cylinder. The dump valve air cylinder ismechanically coupled to the dump valve. There is a pressure sensor influid communication with the water intensification cylinder.Additionally the water intensification cylinder is in fluidcommunication with a water source, the dump valve, and the BOP assembly.In operation an air source, precisely controlled by an automatedpressure regulator and commanded by a computer controller. is directedto the extend port of the primary air cylinder and the extend port ofthe dump valve air cylinder via an air control block to cause both theprimary air cylinder and the dump valve air cylinder to extend. Theaction of the dump valve air cylinder extending causes the dump valve toclose. The action of the primary air cylinder extending causes the waterintensification cylinder to displace water intensification fluid intothe BOP assembly thereby causing a pressure increase within the BOPAssembly. This action of displacing water intensification fluid, causinga pressure increase within the BOP assembly, continues until thepressure within the BOP assembly reaches the desired pressure level.Subsequently to reaching the desired pressure level. the computercontroller precisely controls the air pressure of the system, via theair control block, to maintain the pressure with the BOP assembly at aconstant pressure at or very near the desired pressure. Subsequent tocompleting the test the air pressure is redirected to the retract portof the primary hydraulic cylinder causing the primary hydraulic cylinderto move to the fully retracted position and to the retract port of thedump cylinder, causing the dump valve to open, releasing the testpressure from the BOP assembly.

What is claimed is:
 1. A method of testing for leaks in a portion of ablowout preventer device for an oil/gas well comprising: a. pressurizingthe portion of the blowout preventer to a first pressure level, b.maintaining a constant pressure within the portion of the blowoutpreventer to be tested, and c. measuring any amount of fluid added to orremoved from the pressurized portion of the blowout preventer that isrequired to maintain the pressure within the portion to be tested at aconstant level.
 2. The method as claimed in claim 1 wherein the pressureis maintained constant by a intensifier pump driven by a variabledisplacement hydraulic pump.
 3. The method as claimed in claim 1 whereinthe intensifier pump includes an axially movable piston and the amountof fluid added to or removed from the portion of the portion of theblowout preventer is measured by measuring any displacement of thepiston after the portion of the blowout preventer to be tested has beenpressurized to the first pressure level.
 4. The method as claimed inclaim 1 further including step of raising the pressure within theportion of the blowout preventer to be tested to a second pressure leveland measuring any amount of fluid added to or removed from the portionof the blowout preventer to be tested in order to maintain a constantpressure.
 5. The method of claim 4 including the step of attaching avibration sensor to the portion of the blowout prevent to be tested andrecording the various vibration levels at given intervals as thepressure is increased from the first pressure level to the secondpressure level.
 6. The method of claim 1 further including the step ofdetermining the amount of fluid added or removed as a result of changesof temperature of the portion of the well to be tested.
 7. The method ofclaim 1 wherein the pressure within the portion of the blowout preventerto be tested is initially pressurized by a plurality of intensifierpumps driven by a variable displacement hydraulic pump.
 8. Apparatus fortesting for leaks a portion of a blowout preventer comprising: a. a pumpfor pressurizing the portion of the blowout preventer to be tested, b. avariable pressure motive source for driving the pump, and c. means fordetecting the amount of fluid added to or removed from the portion ofthe blowout preventer after the pressure within the portion of theblowout pump has risen to a given level in order to maintain constantpressure within the portion of the blowout preventer to be tested. 9.Apparatus as claimed in claim 8 wherein the variable pressure motivesource is a variable displacement hydraulic pump.
 10. Apparatus asclaimed in claim 9 including a controller for the hydraulic pump and apressure sensor for sensing pressure within the portion of the blowoutpreventer to be tested, the controller maintaining the pressure withinthe portion of the blowout preventer to be detected at a constant level,in response to signal from the pressure sensor.